1. Field of the Invention
The invention relates generally to ultrasonic surgical instruments and, more particularly, to an improved ultrasonic knife.
2. Description of Related Art
The use of ultrasonic surgical instruments for cutting various types of tissues and/or removal of cement within the body is well known. An ultrasonic surgical instrument commonly comprises a knife blade connected to an ultrasonic oscillation source. The edge of the knife blade is brought into direct contact with the tissue being operated on and vibrated at ultrasonic frequencies. Conventional ultrasonic surgical instruments are used to cut or shatter a variety of living tissues such as the soft tissue found in cataracts, the cartilaginous tissue found around bones, and the osseous tissue of the bone itself. Surgeons are also finding ultrasonics to be an excellent tool for the removal of cements, such as, for example, Polymethylmethacrylate (PMMA), which is frequently used to affix a prosthetic hip joint to the existing femur.
The mechanical oscillation at the end of an ultrasonically vibrated knife blade reduces the amount of pressure required to initiate and propagate a cut or incision which allows the surgeon to concentrate more on the direction of cut. Advantageously, the surrounding tissue experiences minimal stretching and tearing as compared to procedures utilizing conventional stationary blades.
Problems which can be associated with ultrasonic surgery include excessive heat generation, tearing of tissue, or inadvertent cutting of nearby structures. Other problems have been associated with the ergonomics of ultrasonic surgical instruments. Moreover, different surgeons desire different tactile feedback and operating performance. The prior art generally has demonstrated a lack of understanding of the tactile feedback necessary to carefully re-sect different types of living tissues with one particular knife.
Some examples of prior art have attempted to reduce the "thermal footprint" of the ultrasonic cutting tool. For example, in U.S. Pat. No. 5,026,387 issued to Thomas, an ultrasonic surgical cutting tool is disclosed which automatically shuts off upon removal from the tissue. The automatic shut-off switch reduces the time that the surgical cutting knife is vibrating and thus decreases its heat buildup. U.S. Pat. No. 4,188,952 issued to Loschilov et al., discloses an ultrasonic surgical instrument which relies on a pentagonal cross section to reduce the thermal damage to the side surfaces of the tissue being cut because of a smaller area of surface contact. The thermal footprint of an ultrasonic surgical knife is defined by its surface area in contact with the tissue, both frontally and on the sides. In general, the inventions of the prior art had been fairly simple in their approach to reducing thermal footprint of ultrasonic blades and have failed to provide any real sophistication for the design of these tools which is sorely needed.
A need exists for an improved ultrasonic surgical blade which gives better feedback when cutting through various types of tissue and provides enhanced ergonomics to surgeons.